app_queue: delayed state can cause early leavewhenempty ringing

In app_queue, device state changes arrive in event messages and
update the queue member status value.  That value is checked in
get_member_status() to decide that the caller should leave when
there are no available members.  Although event messages can be
delayed by other activity, there is no adverse affect by lagged
status except in one specific case: there is only one available
member, it was just rung, and leavewhenempty is enabled set for
ringing members.  This change adds a direct check of the device
state only under this condition where the caller may be dropped
incorrectly, resolving this issue without affecting performance
of app_queue normally.

AST-1248 #close
Review: https://reviewboard.asterisk.org/r/3595/
Reported by: Thomas Arimont
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Merged revisions 415833 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 415835 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 415836 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@415839 65c4cc65-6c06-0410-ace0-fbb531ad65f3